1. Field of the Invention
This invention relates to the cutting of vegetation and more particularly, it relates to an apparatus for cutting vegetation using a flexible non-metallic line member.
2. Description of the Prior Art
Prior to the Industrial Revolution, mankind was cutting vegetation employing various tools containing cutting edges such as sickles, scythes, scissors and like knife-edged tools. After the Industrial Revolution, the householder established a home having a lawn, garden and like vegetation. After the mid-ninteenth century, the homeowner used lawn care machines which followed basically the concepts of mechanized farming tools such as the reel mower, reaper and side bar cutters. In general, these devices were man-powered. Various types of manually-powered metal knife-edged trimmers and edgers were also available to the homeowner. In the early part of the twentieth century, internal combustion and electrical powered machines became available to the large estate and commercial lawn care artisans.
Smaller types of powered lawnmowers and edgers became available after 1940. Then, the inexpensive gasoline and electric-powered rotary blade lawnmowers, edgers and trimmers became available to both homeowners and commercial workers. In these devices, a metal blade was mounted upon a shaft rotated at several thousand revolutions per minute in a cutting plane. The ends of the blade were sharpened into a knife-like cutting edge. These rotary blade devices cut with a shredding or impact action in contrast with the scissor-like clipping action of the reel lawnmower. However, the economies of manufacture made the rotary-bladed motor-powered lawnmowers, edgers and trimmers readily available at low cost to the public.
The rotary-blade type lawnmowers, edgers and trimmers have one serious defect. This defect resides in the cutting action provided by the heavy metal blade whose cutting edges are traveling at velocities approaching 10,000 feet per minute. The cutting blade has a mass of several pounds, so that the kinetic energy present at the blade's cutting edge is tremendous. The rotating metal blades strike solid objects such as rocks, metal, toys, etc., with great force. As a result, these objects are propelled from the cutting blade at high velocities to cause serious injuries to a human being in their path. Also, direct contact of a foot or other part of a human structure with the rotating blade will cause dismemberment or great mutilation. In the United States within the last few years, there has been anually over 70,000 reported accidents relating to rotary metal-bladed lawnmowers, edgers and trimmers.
Extensive and expensive engineering and experimentation have been performed upon the various types of rotary metal cutting devices to reduce the inherent serious hazard. For example, specially-designed shrouds and dead man controls have been proposed by Industry and governmental agencies in an attempt to reduce the large numbers of serious and disabling injuries. Considerable time has been expended in experimentation to replace the rotary metal blade with a flexible cutting element in rotary lawnmowers, edgers and trimmers. The direct substitution of a resilient rotary blade, such as manufactured of laminated rubber, for rotary metal blades had not been universally successful.
In the early 1960's, a trimmer-edger used a flexible non-metallic line carried on a head rotated within a cutting plane in cutting vegetation. In this device, a relatively low-powered motor rotated a head at relatively high angular speeds and carried a very thin, flexible line of a plastic polymeric material. The device did not succeed operation-wise even in limited trimmer-edger applications because of frequent line breakage, ineffective cutting properties and awkward structures. As a result, these devices found no consumer acceptance as a safe substitute for metal-edge rotary cutting devices.
The utility and structural problems of prior art flexible non-metallic line devices for cutting vegetation were overcome by the inventions which are embodied in U.S. Pat. Nos. 3,708,967; 3,826,068; and 3,859,776. These patents describe apparatus for cutting, trimming and edging vegetation wherein a flexible non-metallic line member of proper length is mounted in a proper head structure to prevent line breakage during operation. The line member has a certain cross-sectional size and a given relationship of peripheral velocity. These features provide a proper, useful and user acceptable device for cutting vegetation. Also, these novel devices provide the most acceptable replacement to rotary metal-blade cutting devices. The cutting devices described in these patents have provided the homeowner and commercial user with vegetation-cutting apparatus using a flexible non-metallic cutting line operated in complete safety to the user and with an optimized cutting efficiency approaching the hazardous metal-blade cutting devices.
These patents show devices provided with structural features which allow the flexible non-metallic line to be selectively extended by manual operation of the user. In example, the user stops operation of the device and manually pulls the line member to a desired extended length. In larger vegetation-cutting apparatus, such as gasoline-powered edgers and trimmers, line extension can be a hindrance to most efficient cutting operation. Frequent line extensions result when the flexible non-metallic line members contact metal or concrete structures which causes fraying and breakage of the line members.
There are a number of prior art devices which are capable of providing the extension of the line member from the vegetation cutter employing flexible non-metallic lines. However, no device of the prior art has the capability of being actuated by the operator during the operation to feed a certain discrete length of line from the rotating head member under direct mechanical control. Then, the line is re-locked automatically within the head member. Excessive amounts of line member cannot be discharged from the rotating head at any time. Other features and results of the present invention in an apparatus for cutting vegetation using a rotating flexible non-metallic line will be apparent from the following discussion.